Applications :
Machine controls, Packaging, Palletizing, Material handling, similar Sequential task as well as Process control
Advantages of PLC :
They are fast and designed for the rugged industrial environment.
They are attractive on Cost-Per-Point Basis.
These Devices are less Proprietary ( E.g.. Using Open Bus Interface.)
These Systems are upgraded to add more Intelligence and Capabilities with dedicated PID and Ethernet Modules.
Disadvantages of PLC :
PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices.
To maximize PLC performance and Flexibility, a number of Optional Modules must be added
PLC Types Nano (Small) Micro (Medium) Large Basic criteria for PLC Types Memory Capacity I/O Range Packaging and Cost per Point
Central Processing Unit It is a micro-controller based circuitry. The CPU consists of following blocks : Arithmetic Logic Unit (ALU), Program memory Process image memory (Internal memory of CPU) Internal timers and counters Flags CPU performs the task necessary to fulfill the PLC functions. These tasks include Scanning, I/O bus traffic control, Program execution, Peripheral and External device communication, special functions or data handling execution and self diagnostics.
Input module These modules act as interface between real-time status of process variable and the CPU. Analog input module : Typical input to these modules is 4-20 mA, 0-10 V Ex : Pressure, Flow, Level Tx, RTD (Ohm), Thermocouple (mV) Digital input module : Typical input to these modules is 24 V DC, 115 V AC, 230 V AC Ex. : Switches, Pushbuttons, Relays, pump valve on off status
Output module These modules act as link between the CPU and the output devices in the field. Analog output module : Typical output from these modules is 4-20 mA, 0-10 V Ex : Control Valve, Speed, Vibration Digital output module : Typical output from these modules is 24 V DC, 115 V AC, 230 V AC Ex. : Solenoid Valves, lamps, Actuators, dampers, Pump valve on off control
Power Supply The power supply gives the voltage required for electronics module (I/O Logic signals, CPU, memory unit and peripheral devices) of the PLC from the line supply. The power supply provides isolation necessary to protect the solid state devices from most high voltage line spikes. As I/O is expanded, some PLC may require additional power supplies in order to maintain proper power levels.
Bus System It is path for the transmission of the signal . Bu system is responsible for the signal exchange between processor and I/O modules The bus system comprise of several single line ie wires / tracks
Sense
the Input Process the Logic Give Output Programmable controller
Inputs
Outputs Machine or Process
Input Module
Processor Memory
Output Modules
Data Output Input Image Table Image Table I:0/6
I:0/6
O:0/7 O:0/7
I:1/4
O:1/5
Input Devices
Output Devices
Ladder Program
I:1/4
I:0/6
O:0/7
I:1/4
O:1/5
Programming Terminal
O:1/5
Mid
- 1970s : Discrete Machine Control Programming Terminal Connection is Point to Point
PLC Programming Language : Connection is Point to Point
I/O
- Relay ladder logic - Flexibility in altering Control system operation
Early
- to - Mid 1980 : Discrete and Process Control
MS - DOS
Reasonable Computer Running PLC Programming Software
PLC Programming Language :
I/O
- Ladder Program - PID - Data Storage
◆
Late 1980’s to early 1990’s : Discrete and Process Control Windows PC running PLC Programming Software Connection in networked allowing Multiple PLC
PLC
I/O
PLC PLC became a part of the developing enterprise resource system
Today : Distributed I/O Modules PLC
Distributed I/O scanner
Data Communication Bus
Distributed I/O modules
Today : Hot Redundant System
TAPS SPLITTERS Remote I/O Network FIBER OPTIC LINK
Remote I/O
Today : Ethernet Technology in PLCs
Workstation
Workstation
Workstation
Workstation
Switched Hub
Controller Controller Controller
Controller
Today : Wireless communication PLC Wireless Modem
Remote Platform Wireless Modem PLC
HMI Display
PC
Siemens
S5 -110U, 115U, 135U S7 - 200, 300, 400
Allen Bradley
Micrologix 1000, 1200, 1500 SLC 5/01, 5/02, 5/03 PLC 5/10, 5/25 and 5/40
Modicon Nano
Micro Premium Quantum
Built in display for I/O (in-rack, AS-i) and Diag
Programming Terminal PC Connection
8 Analog Inputs 1 Analog Output
I/O Modules
Up/Down Fast Counter
Up Counter Unitelway Port for connection of up to 5 Slaves
TSX37-22 PCMCIA communications port PCMCIA memory expansion port
CPU I/O Modules External Power Supply
CPU I/O Modules Power Supply
I/O Modules
CPU
Back plane
The open, manufacturer-independent programming standard for automation is IEC 61131-3. You can thus choose what configuration interface you wish to use when writing your application :
Ladder Diagram Instruction List Function Block Diagram Sequential Function Chart Structured Text
Cost of hardware, software, Integration Engineering, Design, Installation, Start-up and Commissioning, Validation documentation and Execution, Training, Spare parts, Maintenance, System service contract and system life cycle. Reliability, Flexibility, Scalability and Validatability. Ease of Database configuration, Graphics development, Interlocks and Batch processing. Integration of High-level Application. Control Philosophy for Centralized versus Remote Operator Console or both. Compliance with an Industry batch standard such as ISA SP88 and new Communication Protocol.